Model methods when to use self

Rails
1

I am extending my model with some methods. My question is when to and
when not to define the method with self.

example

def sales_value
… all kinds of calculations
end

OR

def self.sales_value
… all kinds of calculations
end

2

The shortest (but not the most correct one) way to describe the
difference is to say that def meth1; end is an object method while def
self.meth2; end is a class method, and you cal them differently:

a = Foo.new
a.meth1
Foo.meth2

But there’s more than that

As for Active Records it depends whether you want a method for an
ActiveRecord instance or for the class

Btw these are Ruby basics, find a good Ruby book/tutorial.

Cheers,
Yury

On 5/11/07, bitterbal [email protected] wrote:

OR

def self.sales_value
… all kinds of calculations
end

–
Best regards,
Yuri L.

3

bitterbal wrote:

I am extending my model with some methods. My question is when to and
when not to define the method with self.

example

def sales_value
… all kinds of calculations
end

OR

def self.sales_value
… all kinds of calculations
end

My answer is the same as Yuri’s, just different words.

If sales_value effects or returns a different value for each row in the
table don’t use self. You would then do this for example

sale = Sale.find(id)
puts “The sales value of sale #{id} is: #{sale}”

If sales_value combines data from some or all rows in the table use
self.sales_value. You might then do this:

sales = Sale.sales_value #note there is no find here
puts “the value of all sales is #{sales}”

4

I am extending my model with some methods. My question is when to
and when not to define the method with self.

Ruby 101 :

class String
  def shuffle
    split(//u).sort_by { rand }.join('')
  end

  CHARS = ("a".."z").to_a + ("A".."Z").to_a + ("0".."9").to_a
  def self.random( len )
      newpass = ""
      1.upto(len) { |i| newpass << CHARS[rand(CHARS.size-1)] }
      return newpass
  end
end

puts String.random(10)
puts "abcdef".shuffle

Alain R.

http://blog.ravet.com/

5

Maybe this will help you.

When you are writing model code you are writing a class. That is
“working class” not “learnstitute class.”

Think of “blue collar” and “white collar” workers. People of the
“blue collar” class work a certain way that is difference from a
“white collar” worker. So you may have people (instances) of “blue
collar” and “white” collar workers.

So you have a Class and some Objects of each class. Both the Class
and the Objects can have methods (referred to as class and instance
methods respectively).

When you are writing your code you are writing a class represented in
the def as “self.”

So…

def self.my_class_method

Can be called on the Class or instances of the class

end

def my_instance_method

Is only available to instances of the class

end

Calling them…

BlueCollarWorker.my_class_method # called on the class
a_person_object.my_instance_method #called on the instance.

On May 11, 6:18 pm, John M. [email protected]

6

Thanks. great example that makes it clear for me.

On May 12, 12:18 am, John M. [email protected]